Safety control mechanism



Oct; 26, 1937. J. EATON 2,097,319.

SAFETY CONTROL MECHANISM Filed May 21, 1935 Inventor: Jo h n Eaton,

ttorneg Patented Oct. 26, 1937 John Eaton, Schenectady, N. Y., assignorto General Electric Company, a corporation of New York Application May21, 1935, Serial No. "535 12 Claims. (01. 200-131) My invention relatesto safety control mechanism and hasfor an important object the provisionof improvements for insuring safe operation of electric circuitcontrolling mechanism,

though not necessarily limited thereto.

Details ofthe construction and operation of one embodiment of myinvention as incorporated in a flame responsive mechanism for an elec-'trically operated fluid fuel burner-apparatus are herein described infull,- clear, concise and exact terms. It is to be understood. however,that my invention is not limited to the details of the construction andapplication of the specific mechanism herein illustrated and describedsince such details are .set forth only for the purpose of insuring athorough understanding of the principles underlying the invention inorder that one skilled in the art may perceive other applications towhich the improved mechanism is suited and may properly adapt themechanism to various conditions of operation.

A specific object of my invention is the provision of improvements incertain aspects of the safety switch mechanism disclosed and claimed inthe copending application of John G. Wemple, Serial No. 5,623, fliedFebruary 8, 1935, which application is assigned to the assignee of thepresent invention.

Other objects of my invention will become evident from the followingdescription taken-in conjunction with the accompanying drawing in whichFig. 1 shows the construction of a thermal responsive electric circuitcontrolling device incorporating my invention; Fig. 2 is an end view ofthe device illustrated in Fig. 1 and shows more in detail theconstruction of my improved friction clutch; Fig. 3 is a detailed'viewof certain features of the device of Fig. 1, and Fig. 4

particularly of the thermal responsive type al-' 43 is "a diagrammaticillustration of the manner of incorporating my invention in the circuitcontrolling mechanism of an electrically operated iiuid fuel burnerapparatus.

Referring to Fig. 4, numeral it designates a 45 vertical type boilerfurnace having a combustion chamber II in the top of which is an openingfor the seating of a burner head unit I! provided with a fuel and airnozzle II and ignition electrodes l4. Fuel atomizing air and primary.com-

50 bustion air are supplied under proper pressures to the nozzle I! by acombined blower compressor unit which is energized from the electricsupply circuit I through the automatic control apparatus represented atH. llsdesignates a room thermostat for initiating operation ofthecontrol apparatus. Details of the structure and arrangement of theelements of the burner and control apparatus above referred to may behad by reference to the following copending applications: H. S.Woodruif, Serial No. 676,651, 5 filed June 20, 1933, for the boilerfurnace Ill; W. O. Lum and J. Eaton, Serial No. 691,320, filed September28, 1933, for the burner head I! W. '0. Lum, Serial No. 553,119, filedJuly 25, 1931, and Serial No. 737,063, flied July 26, 1934, for 10 theblower compressor unit ii; John Eaton, Se-

' rial No. 735,103, filed July 14, 1934, for the controlapparatus l1,and W. N. Mischler, Serial No. 715,631, flied March 15, 1934, for theroom thermostat ll, all of which above enumerated 5 applications areassigned to the assignee of the present invention. A sumcientdescription of the operation of the burner and control apparatus aboveidentified will be given hereinafter for a proper understanding of thepresent invention. It is to be understood, however, that the presentinvention is not limited by, the details of the specific apparatusherein illustrated since such details are included herein only for thepurpose of making clear the construction, application and advantages ofmy improved safety mechanism.

A thermal responsive control switch mechanism embodying my presentinvention is indicated at "and the details thereof are shown in'Figs. land 2. The supporting framework for the mechanism comprises a hollowtubular member 20 having mounted at the top thereof a U-shaped member IIwith legs 22 and 23 upon which. are rigidly mounted side arms 24 and 25,respectively, which side arms extend outwardly from the legs oftheU-shaped'member at approximately right angles to the tubular member.The side arms are in apart horizontally opposed relation to eachotherand the upper 40 portion of side arm 24 is bent inwardlyto provide aflange 26 .while the lower portion of the side arm 25 is bent inwardlyto provide a flange 21. 4

On the flanges 26 and 21, which are in spaced apart vertically opposedrelation to each other, are provided the main circuit controlling means,the function of which will be pointed out hereinafter. An electriccontact 3. is mounted on the lower flange 2,1 and hasa connectionterminal 3| in conductive relation therewith, the ,contact and theterminal being insulated from the flange upon which they are mounted-bymeans of insulatiln washer 32 andinmlation'piate a; A second connectionterminal is indicated by the nuwashers 31 and 36.

adjusting nut 4|.

which'is rigidly mounted on the flange 26 and extends through an openingin the flange 27 with the outer end thereof provided with an The desiredspacing is fixedly maintained by means of lock nut 42.

A movable contact element 43 mounted upon contact bar 44 is arranged formovement be-- tween the fixed contacts 30-and 35 which serve to limitthe movement of the contact element in each direction. Numerals 45, 46and 41 designate electric conductors which are fastened.

to terminals 3|, 34 and 36 respectively and serve as means forconnecting the main circuit con- "trolling contacts 30, 43 and 35respectively in circuit with the control apparatus l'l.

Fig. 2 illustrates in detail the construction of the switch arm employedfor operating the contact element 43 between the fixed contacts 30 and35. The switch arm is made up of two sections which are relativelymovable with respect to each other. One of the sections comprises a pairof lever arms 50 mounted for rotation about a pivot pin 5| which issupported by and exprovided with a stop screw 61 having its head tendsbetween the legs 22 and 23 of the U-shaped member 2|. The lever armsextend outwardly from the pivot in opposed side by side relation to eachother and are rigidly braced apart by means of flanges 52-which extendinwardly from the lever arms and are joined together intermediate thearms. 'Inwardly facing cup-shaped recesses 53 are provided on the freeends of the lever arms and in opposing relation to each other. It ispreferable though not necessary that these recesses be substantiallyconical in form. Ex-.

tending between the lever arms and mounted thereon coaxially of therecesses 53 is a pivot pin .54which in addition to the functions to berelated hereinafter, has the function of aiding in bracing the free endsof the lever arms in rigid spaced apart relation.

The second section of the switch arm comprises a pair of members 55and'56 constructed of molded insulation material and having flatextensions 51 and 58 on the respective ends thereof, which extensionsare joined by means of a pivot pin 60 extending therethrough andfastened securely to the extension 58. This construction provides forrotation of the members 55 and 56 about the pin into side by siderelation'with each other. At points on the members 55 and 56 equallyremote from the pin 66 are outwardly facing spherical shaped bosses 6|and 62 which are designed to fit into the inwardly facing recesses 53 oflever arms 50." Bosses 6| and 62 are centrally drilled in order that themembers 55 and 56 maybe pivotally mounted upon the pin 54 extendingbetween the lever arms 56. The inner faces of the members 55 and 56 areprovided with recesses 63 to receive the ends of compression spring 64which surrounds the pin 54. The ends of the members 55 and 56 remotefrom their pivotal junction are not joined so that spring 64 iseffective to force the members apart and thereby to force the outerbearing surfaces of the bosses 6| and 62 into intimate frictionalengagement with the inner bearing surfaces of the recesses 53.

As a result of the improved switch arm construction described in theimmediately preceding paragraphs, there is secured a high degree ofstructural rigidity with improved uniformity of action of the yieldableconnection between the sections of the switch arm. The braced double armconstruction of the first section prevents side play or movement of thatsection in any direction other than in planes perpendicular to the pivot5|, while the two-member construction of the second section and themanner of joining the same to the first section insures against relatedmovement between the sections in any direction other than in planesperpendicular to the pivot 54. Furthermore, the pressure of the spring64 required to maintain proper relation between the two sections of thearm is less than that which would be required if each section of the armcombined only a single member, and, therefore, greater uniformity andsmoothness of action of the friction clutch connection is assured withless danger of sticking due to excessive temperatures or the presence ofdirt between the bearing surfaces of the clutch.

On top of the member 55 adjacent the extension end 51 thereof isprovided a metallic knife-edge pivot 65 to serve as a mounting for thecontact arm 44 which is provided with a bearing seat 66 for engagementwith the knifeedge pivot. The free end of the member 55 is suflicientlyspaced from the member 55 to provide for a limited rotation of thearm-44 relative to the member 55 about the pivot 65. Bar 44 has anopening on the opposite side of the pivot 65 from the stop screw 61 forthe passage therethrough of an extended portion of the pin 6|] whichjoins the members 55 and 56 together..

This pin 60 is provided at its outerend with a head against which abutsone end of a compression spring 1| -mounted on the pin with the otherend thereof pressing against bar 44 and normally operative: to rotatethe bar about the pivot 65 to force the free end of the bar intoengagement with the stop screw 67.

Knife-edge pivot 65 is provided with a metallic mounting plate 12 havingan electric connection terminal 13 to 'which one end of a flexible lead14 is connected. The other end of lead "is fastened to terminal 34. Itwill thus be seen that pivot 65 and seat 66 serve as auxiliary con tactsfor opening and closing the circuit to contact element 43 from electricconductor 46, thecircuit also including contact bar 44, plate 12;terminal 13. flexible lead 14 and terminal 34.

In the embodiment of my invention herein illustrated the operating meansfor the improved switching mechanism comprises a thermal responsivedevice the details of which are shown for purposes of .illustration onlysince it will be evident to one skilled in the art that the switchingmechanism is adapted for use with other forms of operating means withequal facility and advantages. The thermal responsive device illustratedcomprises a hollow tube of some material having a high coemcient ofexpansion, such as nichrome, which is joined in any suitable manner,such as by means of a screw connection diagrammatically illustrated at16, to the lower end of the tube 26 which forms part of the supportingframework for the switching mechanism. Within the tube 15 is disposed arod of substantially non-expansible material, such as quartz, which hasone end in abutting engagement with the closed end of the tube 15.

aosas 1 9 end an adjustable thrust point Ill. The lower end of theelement 6! which serves to join the bracing flanges 63 of the lever arms66 is provided with 'a bearing seat 62 for the accommodation of thethrust point.

Numeral 83 designates a tension spring having one end fastened to a pin64 which extends between the two lever arms 66. The other end of thetension spring is secured to a clip 86 mounted on the supporting tube 26of the framework. This tension spring acts as a biasing means tending atall times to rotate the lever arms 66 in a clockwise direction, asviewed in Fig. 1, in opposition to the force exerted by the thrust point63 against the seat 62.

The supporting framework of the switching mechanism is mounted in anysuitable manner, as by means of bracket 66 diagrammatically illustratedin Fig. 4, so that supporting tube 20 extends vertically downward withthe heat expansible casing 16 in position .to be subjected to the heatof combustion of the fuel discharged from nozzle I3.

In operation, the control apparatus I1 is normally effective, when theburner apparatus is not in operation,-to establish proper startingconnections preparatory to initiation of operation of the burnerapparatus as described in detail in my previously referred toapplication, Serial No. 735,103. Under these conditions, there being noflame within the combustion chamber of the furnace, the casing I6 of thethermal responsive device is in its contracted state causing the quartzrod 11 and the thrust rod 16 to be thrust upwardly so that the thrustpoint 6|! is forced against the bearing s'efl 62 thereby tending toproduce rotation of the lever arms in a counter-clockwise direction, asviewed in Fig. 1. Consequently, bar is forced upwardly so that contactelement 43 is maintained in abutting engagement with stationary cold"contact 36, and the bearing seat of the bar is maintained in engagementwith the knife-edge pivot 66 so that the bar is rotated in a' clockwisedirection until the free end thereof engages the head of stop screw 61.Under these conditions the circuit is closed from control apparatus ilthrough conductor 41, terminal 36, contact 36, contact element 43, bar44, bearing seat 66, knife-edge pivot 66, plate 1!, terminal 13,flexible lead 14, terminal 34 and conductor 46 back to the controlapparatus l'l.

In response to a call for heat by the thermostat It, control apparatusI1 isenergized from supplycircuit i6 and functions, as set forth in myabove identified copending application, to effect starting up of theblower compressor l6 and energization of the electrodes l4 whereby fueland air are supplied to the nozzle" i3'of the burner head'lf and ignitedto produce flame in the combustion chamber ll of the furnace l0. Uponinitiation of flame in the combustion chamber,

the casing I6 of the thermal responsive device' expands and the forceexerted by the quartz rod 11 and thrust rod 13 in opposition to theaction of the biasing spring "is decreased in accordance with increasein the temperature of combustion. Consequently, spring 33 becomeseffective to produce rotation of lever arms 60 in a clockwisedirection,as viewed in Fig. ,1, about pivot pin 6|. Members 66 and 66 also rotatein a clockwise direction, as a unit with lever arms 60, since relativemovement between the two sections of the switch arm is prevented by thefrictional engagement of the clutch connection bearing surfaces. Contactbar 44 rotates in a clockwise direction as a unit with member 65, theaction of spring H being effective to maintain the auxiliary contacts 66and 66 together and the endof the bar 44- in engagement with the head ofthe stop screw 61.

My improved switching mechanism can be adjusted easily by one skilled inthe art so that a minimum of increase in temperature in the combustionchamber is effective to produce sufficient clockwise rotation of theswitch arm to move contact element 43 from abutting engageratus as setforth in my previously referred to copending application.

Initial engagement of contact element 43 and contact 30 is followed by aslight wiping action therebetween as the two sections of the switch armcontinue to rotate in a clockwise direction as a unit and spring II isslightly compressed to permit rotation of contact bar 44 in acounterclockwise direction about the knife-edge pivot so that the freeend of the contact bar is moved from engagement with the head of thestop screw 61 into engagement with the top of member 65.

With normal friction between the bearing surfaces of the clutchconnection, continued heating of the tube 16 of the thermal responsivedevice and consequent lowering of the thrust point 80 results incontinued rotation of the lever arms 60 in a clockwise direction aboutthe pin 6i under theinfluence oftension spring 83. The forces exerted bythe springs 64 and 1| are such with relation to each other that, undernormal operating conditions, the spring 1| maintains the auxiliarycontacts 66 and 66 in engagement after engagement of contact element 43with contact 30, and the friction clutch connection between the twosections of the switch arm yields to permit relative movement betweenthe two sections. In other words, the switch arm in effect breaks in themiddle and the left-hand section thereof comprising lever arms 60continues to rotate in a clockwise direction while the right-handsection thereof, comprising members 66 and 66, is forced to rotate in acounter-clockwise direction, with respect to the left-hand section,about the pin 64. Upon cessation of combustion in the chamber ll of thefurnace due to shutting down of the burner apparatus in response tosatisfaction of the thermostat II, the casing 16 of the thermalresponsive device contracts and the force exerted by the thrust point 66to rotate the lever arms 60 in a counter-clockwise direction, inopposition to the force exerted by the spring 83, increaseswise rotationof the lever arms 63 to effect movement of the contact element-43 fromabutting engagement with contact 36 into abutting engagement withcontact 35, thereby reestablishing the starting connections for the fuelburner apparatus. During the reverse movement of the lever arms 56, thatis movement of the-arms in the 35. Thereafter upon continued decrease intemperature within the combustion chamber with consequent continuedrotation of the lever arms 56 in the counter-clockwise direction, thefriction 'clutch connection yieldsto afford relative movement betweenthe two sections and thereby con- I tact element 43 is maintained inengagement with contact 35. Thus it will be seen that under normaloperating conditions the switching mechanism provides for operation ofthe main circuit controlling contact. element 43 from engagement withone of the fixed contacts into engagement with the other of the fixedcontacts upon initiation of a change in temperature in the combustionchamber in either direction following a change in temperature in theopposite direction, and also provides for maintaining the contactelement 43 in engagement with either of the fixed contactsuponcontinuation of the temperature change which initially producedengagement of the contact element with the particular fixed contact.Furthermore, the pivotal mounting of the contact bar 44 on the member 55with provision for a slight relativemotion between the two resuits in amaximum wiping action upon engagement of contact element 43 with contactand a minimum of wiping action upon engagement of contact element 43with contact 35. This difference in wiping action is a highlyadvantageous feature of my improved switching mechanism since, as willbe understood by one skilled in the.

art, it is desirable to have a more rapid disengagement of the coldcontacts upon initiation of an increase in temperature than-is the casewith the hot contacts upon initiation of a decrease in temperature.

One of the important safety features of'my improved switching mechanismresides in the fact that if, at any time during rotation of the leverarms 56 in the clockwise direction after engagement between contactelement 43 and contact 30, the friction clutch connection between thetwo sections of the switch arm fails to permit relative movement betweenthe two sections as it should normally do under such circumstances,provision is made for completely shutting down the fuel burnerapparatus. Such failure of the clutch connections to permit the relativemovement may result either from excessive temperature of the elementscomprising the clutch connections or from fouling or corrosion of thebearing surfaces of the clutch. Such sticking of the clutch connectionsat a time when theyshould yield to permit relative movement between thesections of the switch arm would be detrimental and even dangerous. Inmy improved mechanism, such sticking of the clutch connections uponcontinued movement of the lever arms 56 in a clockwise direction due toheating'of the nichrome tube 15 or other reasons, causes the twosections of the switch arm to move as a unit while contact element 43 isrestrained from further movement in the clockwise direction by the fixedcontact 36. Under these conditions the compression spring ll yields topermit disengagement of the auxiliary contacts 65 and 66, thusinterrupting the electric circuit to the main circuit I controllingcontact element 43 to effect deenergization of the control circuit forthe fuel burner apparatus. a

A similar disengagement of the auxiliary contacts 65 and 66 occurs incase of continuation of the clockwise movement of the lever arms 56 pasta predetermined limit. Such excessive movement of the lever arms 50 mayresult from either an excessive expansion of the casing 15 or breakageof a portion of the thermal responsive device, such as the casing 15 orthe quartz rod 11, which would produce unopposed clockwise movementof'the lever arms under the influence of spring 83. The operation of themechanism under such conditions is illustrated in Fig. 3. If, afterengagement of contact element 43 with contact 30, the lever arms 56continue to rotate in a clockwise direction past a predetermined limitwhile the clutch connections permit relative movement between the twosections of the switcharm, the free ends of the members 55 and 56 engagethe pin 84 which extends between the two leverarms 1 50. This preventsfurther relativernovement between'the two sections of the switch arm andconstrains members 55 and 56 to move as a unit 1 with lever arms 50. Theresultant operation is the same as that which occurs'if the clutchconnections stick and prevent relative movement between the two sectionsof the switch arm, which is that the spring ll is compressed and theauxiliary contacts 65 and- 66 are disengaged as shown in Fig. 3.

As will be evident from the foregoing discussion, proper operation ofthe safety mechanism depends chiefly upon the relative forces exerted Tby the two springs 64 and H. Spring II is so selected that the forceexerted thereby is suflicient to maintain engagement between auxiliarycontacts 65 and 66 after engagement of contact element 43 with contact30 so long as the clutch connections between the two sections of theswitch arm function properly under the influence of spring 64 to affordrelative motion between the two sections of the switch arm. On the otherhand, the strength of the spring II should be such that it will permitdisengagement of the auxiliary contacts 65 and 66 if the frictionalforce exerted by the clutch connections in opposition to relative motionbetween the sections of the switch arm exceeds a predetermined amountfor any. reason or if such relative movement is completely prevented asby engagement of the free ends of the members 55 and 56 with the pin 84.

From the foregoing discussion it will be seen that'the improvedswitching mechanism of my present invention not only provides anadditional check upon the operation of the fuel burner apparatus in casethe temperatures of combustion produced thereby exceed predeterminedlimits,

'but provides also an improved fail-safe mach-- and of being adapted forother similar applications, and I therefore, aim to cover by theappended claims all the modifications within the yielding connectiontherebetween for causing movement thereof. as a unit to effect operationof one of said elements into and out of a given limiting controlposition, actuating means therefor including a member operable inopposite directions, means interconnecting said member and the other ofsaid control elements for operating the said one control element intosaid limiting position upon a predetermined operation of said member inone direction and including yieldable means providing for operation ofsaid member in said one direction in excess of said predeterminedoperation to effect relative movement of said.

control elements.

2. Safety control mechanism including in combination a member movable inopposite directions, control means having a pair of relatively movablecontrol elements provided with a spring connection therebetween and oneof said elements provided with a slip clutch connection with said memberto be operated as a unit with said member and the other control elementbetween two limiting-positions of said other element upon the initialreverse movement of said member after movement thereof in eitherdirection and having means for stopping the slip operation of saidclutch connection to effect relative movement between said controlelements after a limited slip operation of said clutch connection upon a.predetermined reverse movement of said member.

3. Safety control mechanism including in combination a control elementmovable into and out of a limiting control position, actuating meanstherefor including a member operable in two til-- rections, meansincluding yieldable force transmitting means interconnecting said memberand said element operative for eifecting movement of said element as aunit with said member, said element being movable into said limitingposiiting position, safety control means and means operative foreffecting operation .of said safetycontrol means in case of cessation ofsuch relative movement between said members and. said element at anytime during such continued movement-of said member.

4. The combination with an electric circuit of control means thereforincluding a pair of mov- 'able elements, actuating means for moving oneof said elements in two directions, means. including yieldable forcetransmitting means interconnecting said elements and operative foreifecting movement of the othefof said elements as a unit with said oneof said elements, means for limiting the movement oi said other elementin one direction, said yieldable force transmitting means normally beingoperative to afi'ord relative movement between said elements uponcontinuation of the movemnt of.said one element in said one directionafter said other element reaches its limiting position, and meansoperative for effecting deenergization of said electric circuit in caseof failure of said force transmitting means to afford such relativemovement between the members at any time during such continued movementof said one element.

5. The combination with an electric-circuit of controlling mechanismtherefor including a member operable in two directions, a second memberpivotally mounted on said first member, means providing a frictionclutch connection between said members including means providingcooperating bearing surfaces on said members and resilient means forforcing said bearing surfaces into intimate engagement, said clutchconnection being normally operative upon movement of said first memberfor eifecting movement of said second member as a unit with said firstmember, a circuit control element mounted on said second member, meansfor limiting the movement of said circuit control element in onedirection, said clutch connection being operative for affording relativemovement between said members upon continued movement of said firstmember in said one direction after further movement of said element isprevented, and means operative for effecting deenergization of saidelectric circuit in case said clutch connection fails to afford suchrelative movement between said members at any time during such continuedmovement of said first member.

6. Electric switching mechanism including in combination a pair ofcontacts relatively movable into abutting engagement, actuating meansincluding a member movable in opposite direca yieldable forcetransmitting device interconnecting said members for producing unitarymovement of said members to effect engagement of said contacts uponinitial movement of said first member in one direction after movementthereof in the other direction, said device 'normally being operative toafiord relative movement between said members upon continuation of themovement of said first member in said one direction after engagement ofsaid contacts, a second pair of cooperating contacts, means normallyoperative for maintaining said second pair of contacts in engagement,and means operatively responsive to cessation of relative movementbetween said members at any time during said continued movement of saidfirst member for effecting disengagement of said second pair ofcontacts.

'7. Electric switching mechanism including in combination a pivotallymounted member, means for rotating said member in either direction aboutits pivotal mounting. a second member pivotally mounted on said firstmember, yieldable means operative for causing said second member to moveas a unit with said first member, a third member pivotally mounted onsaid second member, yieldable means operative for causing said'thirdmember to move as a unitwith said second member, a contact elementmounted on said third member, a pair of contacts fixedly mounted inspaced relation for limiting the movement oi said contact element inboth directions, said first yieldable means being normally operative,for affording relative movement betweensaid first and second membersupon continuation of the movement of said first member in eitherdirection aftermovement of said contact element is prevented by one ofsaid fixed contacts, and a second pair of contacts mounted one on saidsecond member and one on said third member and normally held inengagement by said second yieldable means, said second yieldable meansbeing operative upon cessation of relative movement between said firstand second members at any time during continuation of the movement ofsaid first member in said one direction after further movement of saidcontact element is provided for affording relative movement between saidsecond and third members to thereby effect disengagement of said secondpair of contacts.

8. In an .electric circuit controlling mechanism, the combinationincluding circuit controlling means operable into a plurality ofpositions, and means including an arm movable in opposite directions foractuating said circuit controlling means, said arm including a firstsection having a. pair of members infixed spaced apart side by siderelation, a second section comprising a pair of members joined forrelative movement into side by side relation, means for pivotallyjoining said sections with portions of the members of said secondsection disposed between. the members of said first section andincluding resilient means for forcing the members of said second sectionapart and into contact with the members of said first section, and meansproviding bearing surfaces on the outer faces of the members of saidsecond section for frictional engagement with cooperating bearingsurfaces "P ovided on the inner faces of the members of second sectionhaving a pair of members joined for relative movement into side by siderelation with each other .and with'each of the last referred to membersprovided with a substantially spherically shaped bearing-boss atsubstantially the same distance from the junction between the members,and means for pivotally joining .said sections with the bosses of themembers of said second section engaging the recesses ofthe members ofsaid first section including resilient means for forcing the members ofsaid second section apart to efiect intimate frictional engagementbetween the surfaces of said bosses and the surfaces of said-recesses. V

10. In an electric circuit controlling mechanism, the combinationincluding circuit ,controlling means operable into a plurality ofpositions, and means including an.a rm movable in opposite directionsfor actuating. said circuit controlling means, said arm including a pairof members dly braced in spacedapart side by sidejrejlation to eachother and mounted for rotation about a common axis, a pivot shaftextending between .said members at a point remote from the axis ofrotation thereof, a second pair of members rotatably and slidablymounted on said pivot shaft and pivotally joined to each other at apoint remote from said pivot shaft, means pro- ,viding cooperatingbearing surfaces on the inner faces of said first pair of members andthe outer faces of said second pair of members adjacent said pivotshaft, and resilient means disposed between said second pair of membersfor forcing the same apart to efiect intimate frictional engagementbetween said bearing surfaces.

11. Ina safety mechanism for heating apparatus and the like, thecombination including a member movable in .opposite directions about afixed pivot point, actuating means therefor, a

thereto upon predetermined movement of saidmembers, whereby continuedmovement of said first member in a predetermined direction about itsfixed pivot point by said actuating means first moves all three membersas a unit about ,said pivot point until the third member reaches one ofsaid limits, then moves the first two members as a unit relatively tothe third, the latter moving about the said limit as a pivot, thereafter-moving the first member, relatively-to thesecond and third members as aunit, the latter moving ,about the said limit as a pivot,until themovement of thesecond member with respect to the first is constrained bysaid movement constraining means, and finally moves the firstand secondmembers as a ,unit about the fixed pivot point and the third about saidlimit as a pivot point to effect relative angular movement between thesecond and third members.

12. In a safety control mechanism, the com- .bination includingthree"'n'iembers angularly .movable with respect to each other, thefirst member mounted for movement about a fixed pivot, the secondpivotally mounted on the first,

and interconnected thereto through yieldable force transmitting means,and the third member mounted ,on the second member and adapted to moveangularly thereto, actuating means adapted to act 'on said first memberfor moving all said members, means for limiting the movement 'of saidthird member after a predetermined movement in either direction andadapted to act as a pivot for said member, a first control means carriedby said third member and operable upon initial reverse movement ineither direction" of said actuating means, and second control means-.operable upon a predetermined relatively angular movement between thesecond and third members upon continued movement of said actuating meansafter the latter has been actuated to one of its limiting positions.

' JOHN EATON.

